How can I reset my menus?
Info Header

The Info header is the header bar that contains the File menu option. 

Each window in Blender has a header bar and the type of window is set by the first icon on the left-most side of every header. 

For example, in this picture, the different windows are highlighted in yellow and the Window Type icon for each is highlighted in green:  



In order to change any window from one type to another, just click on the Window Type icon and select the type of window you want to have. In your case, you will need to set one window to Info since it has the File menu option so you can restore the factory defaults by clicking: File > Load Factory Settings. Here is what the Info icon looks like:  



NOTE: It is also possible to hide the header by dragging it's top edge down. This leaves a small grey tab with a + sign in it on the right-hand side of the window. Clicking on this + tab brings the header back into view:  



You can read more about header bars here in the Blender Wiki.

Manually Rearranging Windows

However, you can also manually close windows or open new ones by dragging on the  window splitter widgets (they look like a little ridged thumb grip) in the upper right and lower left corners of every window:  



Here is a demonstration of how to drag the window splitter widgets to open and close different windows, as well as how to change these windows from one type of window to another by changing the Window Type icon:  



You can learn more about how to manually arrange window frames the way you would like them here.

You can also check out the answers here and here.